Image Credit: Rob Sheridan; Albert L. Ortega/PR PhotosThe Social Network doesn’t come out until tomorrow, but it’s already a chart topper—in the music world, at least. The movie’s instrumental score, written by Nine Inch Nails’ Trent Reznor and composer Atticus Ross, is currently at the number one spot on Amazon’s MP3 album chart. Even better, it’s getting rave reviews from fans, including Social Network star Justin Timberlake.

“The score is the best part about this movie,” says Timberlake, who plays Napster co-founder Sean Parker in the film. “[It’s] the most unique and dark and ominous and emotional score that I’ve heard in so long. And if [Reznor] doesn’t get some sort of accolade for that, I will think it’s a travesty.”

So how did director David Fincher get Reznor to score his movie? Turns out they have a history together.

“I’ve known Trent for a long time now,” says Fincher. “We had talked at one point about doing Fight Club on Broadway. We wanted to do this super homoerotic, industrial bridge-and-tunnel affair.”

Still, when Fincher asked Reznor to work on The Social Network, Reznor initially said he was too worn out from touring with Nine Inch Nails to do a film score. So Fincher used excerpts from the Nine Inch Nails’ album Ghosts as a temporary soundtrack during the editing process. “They had this very playful kind of Eno-esque thing,” says Fincher. “I loved how it… used synthesizers and it used a sort of walls of dissonance and sound effects.”

Convinced that Reznor was the man for the job, Fincher persuaded him to look at early footage of the movie.

“The entire time he sat there kind of nodding his head,” recalls Fincher. “At the end of it he said, “Yeah, yeah. Interesting. Ok thanks.” And he got up and left. I thought, well, that’s a bad sign. The only person who says ‘interesting’ is my mom when she doesn’t want to say she doesn’t like something.”

But in this case, “interesting” meant good – Reznor soon sent Fincher a number of “sketches” for the movie’s score, which Fincher assembled with his sound designer and editors. After a few more meetings to tailor the music to specific parts of the movie, the score was finished. The entire process took just four weeks.

Looking back on the experience, Fincher has high praise for Reznor’s work ethic. “You’re talking about a guy who is so profilic, so disciplined in his craft of making what he makes,” says the director. “There’s none of this artistic pretense. He just wants to do it.”